The Five Ways

On the Five Ways of Proving the Existence of God of Saint Thomas Aquinas

The Five Ways of Proving that God Exists — Summa Theologiae Ia, q. 2, a. 3.
(See also Aquinas’ other discussions of God’s existence and his Natural Theology).

Explanations, Analyses and Assessments of the Five Ways

• The Five Ways in Context
• The First Way
• The Second Way
• The Third Way
• The Fourth Way
• The Fifth Way
• (Video Presentations on the Five Ways are available on the Videos Page)

“This Everyone Calls God” – How Aquinas identifies the object of his proofs as the Christian God.

Links to Other Explanations/Analyses of the Five Ways: (arranged in ascending order of detail and sophistication)

• Cosmological Arguments (including Aquinas’) — by Stephen A. Richards
• Revisiting the Argument from Motion (The First Way) by Bp. Robert Barron (Word on Fire Ministries)
• Problems of the First Cause by Fr. William Most, from the electronic library of EWTN.
• Explanation of the First Way — by Philip A. Pecorino.  Also includes other cosmological arguments and objections, especially in the light of Big Bang cosmology.
• To Follow the Second Way of Aquinas — by David McGraw. An explanation of the proof from efficient causality (dynamic punch) and a defense of identifying the First Cause with God. Also includes an impressive list of links to relevant resources on the internet.
• Robert C. Koons, Professor, University of Texas at Austin 
  • “Does the God of Classical Theism Exist?” in Classical Theism: New Essays on the Metaphysics of God, ed. Jonathan Fuqua and Robert C. Koons (Routledge, 2023).
    
    In section 1 below, I will rely on Aristotle’s argument from motion (Thomas Aquinas’s First Way) to argue for the existence of an atemporal being without passive potentiality (characteristics 2 and 3). In section 2, I will turn to Aquinas’s Second Way, attempting to demonstrate the existence of an absolutely first cause (characteristic 1). This will provide additional support for the second and third primary characteristics as well. In section 3, I will take up the question of the analysis of existence provided by Thomas Aquinas in De Ente et Essentia and related passages. This analysis will provide support for all four primary characteristics. Next, I will argue in section 4 that God’s infinity and perfection follow from the primary characteristics, and in section 5 I will try to include the corollaries of God’s unlimited knowledge and power. I will conclude, in section 6, with some thought about whether it would be possible to affirm the existence of both the God of classical theism and that of the Bible, while denying their identity.
  • “Does the Universe Have a Cause?” in Contemporary Debates in Philosophy of Religion, 2nd edition, Raymond VanArragon and Michael Peterson (eds.), Wiley-Blackwell, 2019. (Not about Aquinas per se, but helpful.)
  • “God’s Existence,” in Neo-Aristotelian Perspectives on Metaphysics, Daniel D. Novotny and Lukas Novak (eds.). (Oxford: Routledge, 2013), pp. 247-68.
  • “St. Thomas Aquinas on Intelligent Design,” with Logan Paul Gage, Proceedings of the American Catholic Philosophical Association 85 (2011):79-97.
  • “Ways Two and Three: Thomas Aquinas on the Intelligibility of Being,””Epistemological Foundations for the Cosmological Argument,” in: Oxford Studies in the Philosophy of Religion, Volume 1, edited by Jonathan Kvanvig (Oxford, 2008).

Analysis of Thomistic Proofs in General:

• Aquinas and the Big Bang by William Carroll
• St. Thomas and Big Bang Cosmology by William Carroll
• Creation, Evolution, and Thomas Aquinas by William Carroll
• Can the Existence of God Be Known by Reason? — by James Arraj

Criticisms of Aquinas or Cosmological Arguments:

• The Resurrection of Thomism, by Doug Erlandson. Claims the principle “nothing comes from nothing” is circular and question begging.
  • Reply to Erlandson, by Joseph Magee.

See also “Why the Burden of Proof is on the Atheist,” by Ralph McInerny.

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Updated May 15, 2025